It has been a conventional practice to subject a semiconductor Si substrate to wet cleaning. However, there have been problems that: complete removal of a water mark formed during drying and control of etching of a very thin oxide film cannot be achieved; and an apparatus has an increased size, and like problems. Further, when the semiconductor substrate is exposed to atmosphere for a long time after the wet cleaning of the semiconductor substrate, a surface of the semiconductor substrate forms a native oxide film thereon and adsorbs carbon atoms thereto, which results in problems including: film deposition of an Si single crystal being impossible; formation of a rough surface; and development of an impurity level at an interface with an gate insulating film.
In view of such problems, removal of an oxide film on the surface of the semiconductor substrate has been practiced by UHV vacuum heating at 750° C. or higher or heating in an H2 atmosphere at 800° C. or higher before the film deposition. However, with progressing device miniaturization, a dielectric insulator film metal electrode is employed, which requires that a device be fabricated at a lower temperature. From now on, device fabrication at a temperature equal to or lower than 650° C. will be required. Therefore, the wet cleaning has limitations, and a dry cleaning method becomes necessary for processing the semiconductor substrate prior to the film deposition. An example of such a dry cleaning method is a reverse sputtering method using argon plasma (Japanese Patent Application Laid-Open No. H10-147877). With this method, however, it is considered that an Si—Si bond at the surface of the semiconductor substrate is also broken. In this case, there arise problems that: an oxide film is immediately formed at the Si deficient portion; adhesion of a contaminant substance to a dangling bond of Si is likely; and re-adhesion of oxide and contaminant substance resulting from sputtering to a sidewall occurs, and like problems. This will results in adverse effects on a later process (including impediment to epitaxial growth and formation of a high resistance portion at a silicide interface).
Damage to the device is also problematic. Japanese Patent Application Laid-Open No. 2001-102311 discloses a technique of taking out only a radical by turning a gas containing a halogen or hydrogen into plasma and then cleaning a semiconductor substrate with the radical. However, in cleaning the semiconductor substrate with an H radial, there arise problems including metallic contamination from the chamber used and overetching due to a high etch rate of an Si underlayer. Further, since re-adhesion of HF as a reaction product is likely, a sufficient F removal effect cannot be obtained. In cleaning the semiconductor substrate with an F radical, it has been impossible to remove F remaining on an Si surface and on an SiO2 surface by heating at a temperature equal to or lower than 650° C. because the Si—F bond energy is high. In film deposition (in the case of UHF-epi) over the semiconductor substrate by allowing a material gas (SiH4 gas) to flow over the semiconductor substrate in that condition, a problem has arisen that variations in incubation time (i.e., a time period until film deposition over the surface starts actually) occur between batches. Such variations make a time control of film thickness difficult between batches. Japanese Patent Application Laid-Open No. 2001-144028 discloses a technique of removing fluorine residue by exposing a semiconductor substrate to plasma containing fluorine-containing species to clean the substrate and then exposing the semiconductor substrate to an atmosphere which captures fluorine. The fluorine capturing atmosphere is prepared by plasma decomposition of a gas containing hydrogen-containing species.
However, since the semiconductor substrate is exposed to plasma, the Si—Si bond is also broken. In this case, there arise problems that: an oxide film is immediately formed at the Si deficient portion; adhesion of a contaminant substance to a dangling bond of Si is likely; and re-adhesion of oxide and contaminant substance resulting from sputtering to a sidewall occurs. This will results in adverse effects on a later process (including impediment to epitaxial growth and formation of a high resistance portion at a silicide interface). Damage to the device is also problematic. According to this known example, the gas is forcibly decomposed with plasma to generate a hydrogen group (i.e., H radical) and hydrogen ions. In removing fluorine residue remaining on the substrate surface by the hydrogen group (i.e., H radical) and hydrogen ions, there arise problems including metallic contamination from the chamber used and overetching due to a high etch rate of an Si underlayer. Further, since re-adhesion of HF as a reaction product is likely, a sufficient F removal effect cannot be obtained. Japanese Patent Application Laid-Open No. 2002-217169 discloses an apparatus which carries out a cleaning process for removing foreign matter in-situ by combination with a physical action of a frictional stress caused by a high-speed gas flow. According to the description of this known example, adsorption of impurities and occurrence of native oxidation are suppressed by transport under vacuum, which leads to an improved production efficiency. However, even though the foreign matter can be removed, a native oxide film and surface roughness remain on the surface atomic layer order. That is, in order to obtain the effect of improving the device characteristics by transport in-situ, it is necessary to provide a cleaning technique capable of controlling a surface on the atomic layer order, a technique of terminating the surface with a desired atom, and a technique of transport without exposure to atmosphere for film deposition. With these techniques, it is considered that favorable device characteristics can be obtained including reduced interface states at a semiconductor/dielectric insulator junction and reduced fixed charges in the film.
Patent Document 1: Japanese Patent Application Laid-Open No. H10-147877
Patent Document 2: Japanese Patent Application Laid-Open No. 2001-102311
Patent Document 3: Japanese Patent Application Laid-Open No. 2001-144028
Patent Document 4: Japanese Patent Application Laid-Open No. 2002-217169